Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Series E Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series E Preferred Stock [Member]	Treasury Stock, at cost [Member]	Accumulated Other Comprehensive Loss, Net of Tax [Member]
Beginning Balance at Dec. 31, 2015	$ 2,413,960		$ 122,710	$ 937	$ 1,124,325	$ 1,315,948		$ (71,854)	$ (78,106)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	97,650					97,650
Other comprehensive income, net of tax	20,595								20,595
Dividends and dividend equivalents declared on common stock $0.25 and $0.23 per share during the 3 months ended March 31, 2017 and 2016, respectively	(44,054)				70	(44,124)
Dividends on Series E preferred stock $400.00 per share for the 3 months ended March 31, 2017 and 2016		$ (4,048)					$ (4,048)
Stock-based compensation, net of tax impact	7,642				2,265	123		5,254
Exercise of stock options	1,773				(1,051)			2,824
Common shares acquired related to stock compensation plan activity	(5,183)							(5,183)
Common stock repurchase program	(11,206)							(11,206)
Common stock warrants repurchased	(163)				(163)
Ending Balance at Jun. 30, 2016	2,476,966		122,710	937	1,125,446	1,365,549		(80,165)	(57,511)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair Value	4,125,125
Beginning Balance at Dec. 31, 2016	2,527,012		122,710	937	1,125,937	1,425,320		(70,899)	(76,993)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	121,050					121,050
Other comprehensive income, net of tax	4,911								4,911
Dividends and dividend equivalents declared on common stock $0.25 and $0.23 per share during the 3 months ended March 31, 2017 and 2016, respectively	(47,058)				82	(47,140)
Dividends on Series E preferred stock $400.00 per share for the 3 months ended March 31, 2017 and 2016		$ (4,048)					$ (4,048)
Stock-based compensation, net of tax impact	7,951					1,118		6,833
Exercise of stock options	4,591				(1,358)			5,949
Common shares acquired related to stock compensation plan activity	(9,283)							(9,283)
Ending Balance at Jun. 30, 2017	2,605,126		$ 122,710	$ 937	$ 1,124,661	$ 1,496,300		$ (67,400)	$ (72,082)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair Value	$ 4,197,378